A report says that laughing or crying at inappropriate moments, or out of context to one's circumstances, can signal underlying illnesses like multiple sclerosis, Parkinson's disease and Alzheimer's disease.
An MSNBC.com report cites an example of a naval aviator student who would break out into hysterical laughter during odd moments. He would also laugh in his sleep in the middle of the night. Later, it turned out, that he was suffering from a rare form of epileptic episode called gelastic seizure, reports the New York Daily News.
According to Robert Provine, author of "Laughter: A Scientific Investigation" and a psychology professor at the University of Maryland, Baltimore County, tagging ill-timed outbursts of laughing or crying an involuntary emotional expression disorder isn't quite right.
"All laughter is uncontrollable in the sense that we don't laugh, or cry, on command," he says. "Laughter is really unconsciously controlled. We go through life making these uncontrollable utterances."
"We can try to stop laughing since it can get us into trouble when we laugh at the wrong time," Provine says. "But it's very hard to produce convincing laughter on command."